[Aneurysmal bone cyst of the ethmoid. Apropos of a case].

Repeated epistaxis in a 12 year old child revealed an aneurysmal bone cyst of ethmoid, an exceptional localization for this lesion. Modern imaging techniques (CT scan, NMR) provided precise data on its extent, primordial for decision as to surgical approach. NMR imaging was more effective than the CT scan for diagnosis, since blood lakes were identified, and for determination of extent, since tumoral elements were distinguished from sinusal retentions.